The systems or stations for adjusting the pressure on several lines are basically plants which allow networks to be fed for carrying and distributing gas to civil and industrial users.
Purely by way of example, systems for adjusting the pressure are used in distribution networks for reducing the gas pressure from medium pressure to low pressure.
With reference to the standards currently in force in Italy, low feed pressure means a pressure between 0.04 bar and 12 bar, medium feed pressure means a pressure between 12 bar and 24 bar, and above this one speaks of high pressure.
The reference to “two or more lines” in the above-mentioned adjusting systems refers to the fact that they usually consist of several pressure adjusting lines arranged in parallel.
Of these lines, one is generally referred to as “main”, as it is normally operational, and the others are referred to as “secondary”, as they are normally inactive and designed to enter into operation in the case of a fault or malfunction of the main line.
The main and secondary lines are calibrated differently and, if the main line is no longer able to feed gas at the calibration pressure, the secondary lines activate automatically, feeding gas at the relative calibration pressure, which is lower than that of the main line.
Gas distribution firms are starting to make low cost and fully automatic apparatuses for equipartition of the flow that allow the two or more existing lines to be always run in parallel with a flow of gas equipartitioned and substantially equal.
In short, this modification theoretically allows the achievement of many advantages.
A first advantage would be a considerable lowering of the noise level since the flow of gas would be divided between several lines.
Another advantage would be always having in operation the lines, to prevent the problems of sticking of the seals (O-rings) which sometimes occurs when, following a fault on the main line, an emergency line (secondary) must intervene after long periods of inactivity. The problem of sticking of the O-rings is caused by the prolonged inactivity of the apparatuses, a problem which would be resolved by making the lines normally operating.
Another advantage that would be achieved by making several lines operate in parallel would be that of not having to design the lines to operate, for example in the case of two lines, one at 100% and the other at for example 70% but it might, instead, be possible to design both lines to each cover 50% of the total flow. In this way there would be considerable savings also in terms of costs and installation spaces, moreover being able to overcome any faults in the lines by adopting a grid architecture of the current gas distribution networks.
There are prior art devices designed to manage the equipartition of the flow between various lines in parallel but these devices are not free from drawbacks. A first of these drawbacks is due to the fact that they require, so as to be able to control the adjusting devices of the various lines, one or more additional control units, thereby complicating the architecture of the adjusting system and consequently increasing both the plant and management costs.
Another drawback is due to the impossibility of guaranteeing, at least in the case of a fault on the main line, an adequate and safe operation of the remaining parts of the plant.
Another drawback resulting from the introduction of additional control units, in addition to the management complexity, is due to the need to alter the existing service parameters such as, for example, the calibration values of the original control units.
A solution of this type is illustrated in patent document WO2012153310 wherein an additional control line is positioned in parallel with the standard controls combined with each pressure adjusting device.